1. Technical Field
The present invention generally relates to a developing device to develop images by generating an alternating electrical field in a development range and further relates to an image forming apparatus, such as, a copier, a printer, a facsimile machine, a plotter, or a multifunction peripheral (MFP) having at least two of coping, printing, facsimile transmission, plotting, and scanning capabilities, that includes the developing device.
2. Description of the Background Art
In electrophotographic image forming apparatuses, such as copiers and printers, after being uniformly charged, the surface of a latent image bearer is exposed with light, thereby forming an electrostatic latent image thereon. The electrostatic latent image is then developed into a toner image. The toner image is transferred onto a sheet of recording media either directly or via an intermediate transfer member.
Various development types have been proposed so far. Specifically, there are direct voltage development and alternating voltage development, and differences in properties of developer exhibited in direct voltage application and alternating voltage application respectively are used to attain high image quality. Additionally, there are multiple developer types, namely, one-component developer and two-component developer, and development type further depends on the transfer type of developer to the latent image bearer in the development range, either direct contact or contactless. Yet additionally, distinctive latent image bearers and distinctive developer bearers have been developed, and new development methods using them are proposed to fulfill performance of the image forming apparatus with the combination of developer properties and the development methods. In particular, the following approaches in alternating voltage development have been proposed.
For example, JP-2003-287961-A proposes an image forming apparatus in which, while merits of alternating voltage development are maintained by increasing a frequency f and a peak-to-peak voltage Vpp of alternating voltage used as development bias, demerits such as image disturbance and scattering of two-component developer to a photoreceptor drum are inhibited. It is proposed that, in this image forming apparatus, the frequency of the alternating voltage applied to a developing sleeve is within a range from 4 kHz to 7 kHz, and the peak-to-peak voltage of the alternating voltage is within a range from 1.5 kV to 2.5 kV.
Additionally, JP-2000-347507-A proposes an image forming apparatus designed aiming at suppressing background stains and the occurrence of absence of toner at the rear end of a recording medium (hereinafter “rear-end void”). Specifically, in this image forming apparatus, development bias has a frequency f within a range from 5 kHz to 15 kHz, and the amplitude Vpp (kV) of the alternating component of the development bias is reduced cyclically. JP-2000-347507-A discloses evaluation results regarding background stains, rear-end void, and granularity in an experiment for effect confirmation in which the frequency f of the alternating component of the development bias is varied within a range from 0 to 20 kHz.
According to the disclosed results, background stains are inhibited as the frequency f increases toward 20 kHz. Rear-end void and granularity, however, worsen as the frequency f increases toward 20 kHz.